1. Field of the Invention
The present invention relates to a continuous passive motion device and, more particularly, to an orthopedic device for the continuous passive exercising of limbs for therapy, rehabilitation or healing.
2. Description of the Prior Art
It has been known for many years that the slow, continuous flexing of a joint, such as the knee, following surgery on that joint will promote rapid healing, reduce pain during healing and result in an increased range of motion of the joint when healing is completed. Thus, in the medical specialty of orthopedics, devices for the continuous passive exercising of limbs for therapy, rehabilitation or healing are known. This continuous passive motion is usually applied to a frame which cradles the leg within it, while the frame is driven slowly up and down with an electric motor and drive screw. The drive mechanism is usually located beneath the leg, with the leg raised at an angle of from 6.degree. to 15.degree. in order to clear the motor and drive screw beneath. This has caused difficulty as it is sometimes preferable to have the leg in a near horizontal position when it is straight.
Another problem results from the limited distance between the hips and foot of a standard hospital bed. The usual method of driving the device is to impart a force to the area of the foot, moving it horizontally toward the buttocks. Since the distance the foot must travel in order to fully flex the knee is between 20 and 30 inches, this requires a mechanism of this length or longer. This results in great difficulty in containing the length within the restricted length of a standard hospital bed.
Another problem which is incurred is that of setting and controlling the angle of flex. In the early stages of treatment, such as immediately following surgery, it is often desirable to have a small flex angle, i.e. a total of 40.degree., between 20.degree. and 60.degree.. The logical place to measure and control the flex angle is at the knee joint. However, since this is a moving joint in the orthopedic device, problems arise when using it for control purposes. Previous designs have installed potentiometers in the knee joint which give out a voltage commensurate with the angle. This voltage is then fed through a wire to another location where two other potentiometers have been located as part of a control unit. These control potentiometers can then be set at two given points so as to produce output voltages corresponding to the high and low voltages emanating from the potentiometers located at the knee joint. When there is a match between the voltages emanating from the potentiometers located at the knee joint and the control potentiometers, a circuit causes the voltage to the drive motor to reverse, reversing the direction of motion of the device. A voltage meter is then used to indicate the angle of the knee joint as a function of the voltage emanating from the potentiometers located at the knee joint. In actual use, certain inaccuracies have been found inherent in such a system which converts voltages to angular measurements.
It is also desirable to provide a device which is simple, lacking in complexity, and permits the patient to keep his legs close together so that it is comfortable and convenient to use. For one reason or another, available devices have not satisfied this requirement. Typical of the available devices are those described in U.S. Pat. Nos. 2,763,261, 4,089,330 and 4,323,060.